通過多個鍵減少對象數組並將它們推入子集數組

Question

我有以下 object：

const array = [
    {city: 'Auckland', country: 'New Zealand', date: '2024-02-03T00:00:00'},
    {city: 'Manchester', country: 'United Kingdom', date: '2024-02-04T00:00:00'},
    {city: 'Manchester', country: 'United Kingdom', date: '2024-02-09T00:00:00'},
    {city: 'Edinburgh', country: 'Scotland', date: '2024-02-05T00:00:00'},
    {city: 'Manchester', country: 'United States', date: '2024-02-03T00:00:00'},
    {city: 'Manchester', country: 'United States', date: '2024-02-09T00:00:00'}
]

我希望它像下面這樣分組：

{
    city: 'Auckland',
    items: [
        {city: 'Auckland', country: 'New Zealand', date: '2024-02-03T00:00:00'}
    ]
},
{
    city: 'Manchester',
    items: [
        {city: 'Manchester', country: 'United Kingdom', date: '2024-02-04T00:00:00'},
        {city: 'Manchester', country: 'United Kingdom', date: '2024-02-09T00:00:00'}
  ]
},
{
    city: 'Edinburgh',
    items: [
        {city: 'Edinburgh', country: 'Scotland', date: '2024-02-05T00:00:00'}
    ]
},
{
    city: 'Manchester',
    item: [
        {city: 'Manchester', country: 'United States', date: '2024-02-03T00:00:00'},
        {city: 'Manchester', country: 'United States', date: '2024-02-09T00:00:00'}
    ]
}

我嘗試了多種不同的方法。 我在 .net 上搜索了類似的線程，尤其是在此處，但沒有找到類似的線程。 我試過以下方法：

array.reduce((r, item) => {
    r[item.city] = r[item.city] || []
    r[item.city].push(item)

    return r
}, Object.create(null))

但是，這顯然沒有考慮“國家”。 我也嘗試了以下但只返回所需組中的第一項：

    const cities = {};

    for (let p of array) {
      const { city, country } = p;
      const groupByCity = JSON.stringify([city]);
      const groupByCountry = JSON.stringify([country]);
      if (!(groupByCity in cities)) {
        cities[groupByCity] = { city: city, items: []};
        cities[groupByCity].items.push(p);
      } else if (groupByCity in examCities && cities[groupByCity].country !== p.country) {
        cities[`${groupByCity}2`] = { city: city, items: []};
        cities[`${groupByCity}2`].items.push(p);
      }
    }

Answer 1

有很多方法可以做到這一點，這是我使用 reduce 和 map 的方法：

 const array = [{ city: 'Auckland', country: 'New Zealand', date: '2024-02-03T00:00:00' }, { city: 'Manchester', country: 'United Kingdom', date: '2024-02-04T00:00:00' }, { city: 'Manchester', country: 'United Kingdom', date: '2024-02-09T00:00:00' }, { city: 'Edinburgh', country: 'Scotland', date: '2024-02-05T00:00:00' }, { city: 'Manchester', country: 'United States', date: '2024-02-03T00:00:00' }, { city: 'Manchester', country: 'United States', date: '2024-02-09T00:00:00' } ] const result = Object.entries(array.reduce((acc, curr) => { const key = `${curr.city}|${curr.country}` return {...acc, [key]: key in acc? [...acc[key], curr]: [curr] } }, {})).map(([key, value]) => ({ city: value[0].city, items: value })) console.log(result)

基本上，我按{city}|{country}對它們進行分組，並使用reduce形成一個 object ，然后使用map將該 object 轉換為所需的數組。